For vehicles that include passive restraint systems, it is important to be able to determine when an impact event is serious enough to warrant deployment of one or more of these passive restraints in order to protect the vehicle occupants. These may take the form of front airbags, side airbags, seat belt pretensioners, etc. Likewise it is also important to determine when an impact event does not warrant deployment to avoid unnecessary use of the passive restraints, in order to avoid replacement expenses or risks to the vehicle occupants. Additionally, the deployment decision must be accomplished a very short time after vehicle impact. This is preferably accomplished while minimizing the expense of the system.
One current system for determining vehicle impacts involves the use of a single point acceleration sensor connected to a central processor that evaluates the acceleration signal. It is more cost effective than other types of impact sensing in that it generally only requires one sensor, but it must infer the type and severity of impact being detected in order to accurately and quickly make a deployment decision for the passive restraints. The manipulation and calculations made with the acceleration signal then, are key to an accurate deployment decision early in an impact event.
In many applications of the single accelerometer type of system, then, an approach is employed where the integral or energy contribution in a velocity change based calculation is the basis for the actuation decision. Since the energy contribution is largely determined by the low frequency portion of an acceleration signal, the high frequencies are filtered out and ignored. This type of strategy, however, while being able to determine the severity of the impact, will make deployment decision without distinguishing very well between different types of impacts, which may have different deployment decisions for different levels of energy involved in the impact, given the short time frame in which the decision must be made.
It is thus desirable to be able to employ an accelerometer based impact detection and passive restraint deployment system with improved accuracy in the deployment decision.
Also, when one is adapting the particular sensing system for a new vehicle it is preferable to minimize development time and expense by being able to employ non-destructive testing to determine the deployment thresholds for various types of vehicle impacts.